1. Field of the Invention
The present invention relates to an optical digital holding apparatus for holding instantaneous digital information borne by an optical signal.
2. Related Background Art
Instead of digital electronic techniques such as electronic computers, a digital optical technique which uses light instead of electrical signals to attain high speed operation has been drawing attention. In the digital optical technique, the current goal is to construct a digital optical computer. Various methods and apparatus have been proposed and tested for optical digital elements which form the basic configuration of the digital optical computer. One of the required optical digital devices for such an optical digital system is an optical digital holding apparatus which holds instantaneous digital information borne by an optical signal.
Conventional optical digital holding apparatuses which have been proposed and tested are as follows.
(1) A first conventional optical digital holding device uses a method in which an intensity of an external light irradiation to the non-linear optical absorptive material in the etalon resonator is varied to control the transmittance thereof having a hysteresis characteristic.
(2) A second conventional optical digital holding device uses a method in which a nonlinear optical absorptive region is formed in an etalon resonator of a laser diode (hereinafter called LD), and is irradiated with the light to enhance the transmittance to generate laser oscillation.
(3) A third conventional optical digital memory device uses a method in which a light transmitted through an electro optical crystal is received and converted into electrons and this electric signal is transmitted so that it is a positive feedback to the electro optical crystal.
(4) A fourth conventional optical digital holding device uses a method in which an output light of an LED or and LD is received in a photo diode (PD), and an output electric signal of the PD is returned.